Machine tool, especially a hand machine tool

ABSTRACT

The invention is based on a power tool, in particular a hand power tool, with a drive motor ( 12 ) disposed in a housing ( 10 ) and at least one adjusting device ( 14, 16 ), which can be used to durably set at least one parameter of the drive motor ( 12 ) and/or of a transmission during an operating phase.  
     The invention proposes that the adjusting device ( 14, 16 ) have a reset unit ( 18, 20 ), which resets the adjusting device ( 14, 16 ) to a starting position depending on at least one operating parameter.

PRIOR ART

[0001] The invention is based on a power tool, in particular a handpower tool, as generically defined by the preamble to claim 1.

[0002] For most power tools, in particular hand power tools, it isadvantageous to be able to vary a drive speed of the drive motor. Inhand power tools, it is known to use a control unit to keep the drivespeed as constant as possible independent of the load, or to variablyadjust the drive speed by means of an adjusting device.

[0003] For the adjustment, the operator is frequently provided with anadjusting wheel that can be used to durably set the speed and can limitthe speed to a maximal value. The adjusting wheel can also be combinedwith a potentiometer in the switch trigger so that the adjusting wheelpresets the upper limit of the trigger range.

[0004] The adjusting wheel can, for example, be used to match the speedto a machining procedure or to a material to be machined. An operatorcan preselect a speed that can be kept constant while machining a workpiece, for example when sawing, grinding, etc.

ADVANTAGES OF THE INVENTION

[0005] The invention is based on a power tool, in particular a handpower tool, with a drive motor disposed in a housing and at least oneadjusting device, which can durably set at least one parameter of thedrive motor and/or of a transmission during an operating phase.

[0006] The invention proposes that the adjusting device have a resetunit, which resets the adjusting device to a starting position dependingon at least one operating parameter. Operating errors can be reliablyprevented, particularly if the power tool is used by a number of people.The reset unit can advantageously always reset the power tool to astandard operating position from which each operator can start in orderto adjust the power tool in the usual manner for his specific intendeduse. This reliably prevents a new user from overlooking a specialadjustment that is unsuited for a particular intended use. Depending onthe power tool, it can be advantageous that in the starting position,the power tool can be operated with a maximal possible parameter, whichcan then be reduced by means of the adjusting device, that in thestarting position, the power tool can be operated with a minimallyadjusted parameter from which an adjustment should always be started forsafety reasons, or that in the starting position, the power tool can beoperated with a parameter that lies between a maximal and a minimalparameter.

[0007] In power tools, frequently a speed of the tool is crucial to anadvantageous machining; to this end, the adjusting device can preferablyset a maximal speed as the parameter, either directly by means of thedrive machine and/or possibly also by means of a transmission. Besidesthe maximal speed, it can also be useful in principle to use theadjusting device to establish a minimum speed, which should not beundershot during use.

[0008] In addition to a speed, other parameters deemed appropriate byone skilled in the art can also be embodied so that they can be adjustedby means of the adjusting device, such as a minimal and/or maximaltransmitted torque and/or an operating stroke, for example in a sabersaw or an eccentric grinder, etc.

[0009] In another embodiment of the invention, the reset unit resets theadjusting device depending on a period of downtime. A resetting can beachieved in a structurally simple, properly functioning manner.

[0010] If the reset unit can be used to adjust the period of downtimeafter which the reset unit resets the adjusting device, then the powertool can also be adjusted for different fields of application and anunintentional resetting can be reliably prevented; the period ofdowntime is preferably between one and twenty minutes.

[0011] In another embodiment, the invention proposes that the reset unitreset the adjusting device when a power supply is interrupted, forexample when a power plug is pulled or when a battery is being changed.Since in particular a power plug of a hand power tool is frequentlyunplugged or the power supply is interrupted before a change ofoperators, the change of operators can be detected with a particularlyhigh degree of probability.

[0012] Furthermore, there are other conceivable operating parameters,which may be deemed appropriate by one skilled in the art and dependingon which the reset unit resets the adjusting device, for exampledepending on temperature values. The adjusting device can be reset assoon as the power tool has cooled, for example in that a bimetal elementreleases a detent connection, and/or the adjusting device can be resetif a particular temperature is exceeded, for example in the event of anoverload.

[0013] A mechanical reset mechanism can be embodied in a structurallysimple and inexpensive manner, particularly through the use of aprestressed spring element, which is secured in its position duringoperation, for example by means of a detent mechanism that is coupled toan on-off switch and is released when the power tool is switched off.

[0014] If the reset unit has an electromagnetic adjusting element, theresetting procedure can simply be advantageously coupled to a powersupply, for example in that when there is a supply of power, anelectromagnet can—directly or by means of a detent mechanism —prevent areset spring from resetting the adjusting device. If the power supply isinterrupted and an attraction force of the electromagnet is neutralized,then the reset spring resets the adjusting device. Besides a mechanicalreset spring, the electromagnetic adjusting element can also be combinedwith other mechanisms deemed appropriate by one skilled in the art, forexample electrical and/or hydraulic actuators.

[0015] In another embodiment, the invention proposes that the adjustingdevice have at least one electronic unit, which is for setting theparameter and can be reset by the reset unit. The resetting process canadvantageously be coupled to a power supply in the same way as with anelectromagnetic unit. Furthermore, the electronic unit can be embodiedin a particularly space-saving, lightweight, and inexpensive manner. Amechanical resetting of an adjusting element, e.g. of an adjustingwheel, can be advantageously avoided.

[0016] The embodiment according to the invention can be used in variouspower tools deemed appropriate by one skilled in the art, in particularin hand power tools that are used by a number of operators, for examplehand power drills, percussion drills, hammer drills and/or chiselhammers, screwdrivers, right angle grinders, eccentric grinders, saws,planes, etc.

DRAWINGS

[0017] Other advantages ensue from the following description of thedrawings. Exemplary embodiments of the invention are shown in thedrawings. The drawings, the specification, and the claims containnumerous features in combination. One skilled in the art will alsosuitably consider the features individually and will unite them intoother appropriate combinations.

[0018]FIG. 1 shows a schematically depicted hand power drill,

[0019]FIG. 2 shows an adjusting wheel with an electromagnetic resetunit, and

[0020]FIG. 3 shows an adjusting wheel with an electronic control unit.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0021]FIG. 1 shows a hand power drill with an electric motor 12 disposedin a housing 10. The hand power drill can be turned on and off with aswitch 28. For adjusting the speed, the hand power drill has anadjusting device 14 with an adjusting wheel 30, which can be used to seta speed to a particular value. The switch can also be equipped with apotentiometer, which permits it to vary the speed, for example, from 0to an end value preselected by means of the adjusting wheel.

[0022] According to the invention, the adjusting device 14 has a resetunit 18, which resets the adjusting device 14 to a starting positiondepending on an operating parameter as soon as a power supply isinterrupted (FIG. 2). The adjusting wheel 30 is supported so that it canrotate in a housing part 34 by means of an axle 32, which also permits apotentiometer, not shown, to rotate. The axle 32 is secured in thehousing part 34 axially in relation to the adjusting wheel 30 by meansof a gear 36 fastened to the axle 32 and is secured axially in relationto the gear 36 by means of a flange 38 on the adjusting wheel 30. Ahelical spring 22 is supported on the flange 38 and, with a first leg42, engages in a form-fitting manner in the rotation direction betweentwo pins 44, 46 fastened to the adjusting wheel 30 and with a second leg48, engages in a form-fitting manner between two pins 50, 52 fastened tothe housing part 34.

[0023] If the hand power drill is connected to a power supply by meansof a power plug that is not shown and a power cable, then anelectromagnet 24 is supplied with current and moves a ram 54 into atooth gap of the gear 36. If the adjusting wheel 30 is turned in orderto limit a maximal speed that can be set by the switch trigger 28 to aparticular value, then the ram 54 can be moved out of its detentposition in the gear 36 i.e. out of a tooth gap, counter to the magneticforce of the electromagnet 24. If a tooth gap of the gear 36 comes torest over the ram 54, then the magnetic force of the electromagnet 24moves the ram 54 into the tooth gap. The adjusting wheel 30 can be movedin steps that are predetermined by the tooth gaps of the gear 36. If adesired step or a desired speed limitation is achieved, then theadjusting wheel 30 and the potentiometer are immobilized by means of theaxle 32, the gear 36, and the ram 54 of the electromagnet 24 engaging inthe tooth gap of the gear 36. Moving the adjusting wheel 30 places thehelical spring 22 under stress.

[0024] If the power plug is pulled after an operating phase, and thepower supply to the electromagnet 24 is interrupted, the helical spring22 can move the ram 54 out of the tooth gap of the gear 36. The helicalspring 22 resets the adjusting wheel 30 and the potentiometer into theirstarting positions and the speed limitation is cancelled so that thehand power drill can be operated at a maximal possible speed by means ofthe switch trigger 28. The gear 36 and the electromagnet 24 with the ram54 advantageously serve to graduate the adjusting range of the adjustingwheel 30, to lock the adjusting wheel 30 during an operating phase, andto advantageously embody a reset mechanism.

[0025]FIG. 3 shows an alternative adjusting device 16 with an adjustingwheel 56. In principle, components that remain essentially the same arelabeled with the same reference numerals. For features and functionsthat remain the same, the reader should refer to the description of theexemplary embodiment in FIGS. 1 and 2.

[0026] The adjusting wheel 56 is connected by means of a pulse generator58 to an electronic control unit 26, which provides a speed governor 60with a set point value. Instead of a pulse generator, however, it isalso possible to provide an endless potentiometer. If the hand powerdrill is connected to a source of current by means of a power supply 62with a power plug and a power cable, then a line 64 supplies the controlunit 26 with current independent of the actuation of the switch 28. Theadjusting wheel 56 can then be used to adjust the speed of electricmotor 12 to a particular value. The adjusted speed is indicated on adisplay 66. If the adjusting wheel 56 has reached an adjusting limit inone of its rotation directions, the adjusting wheel 56 can be rotatedfurther without changing the speed setting.

[0027] If the power plug is pulled and the supply of current to thecontrol unit 26 is interrupted or if a particular period of downtime hasbeen reached, i.e. the hand power drill has not been actuated for aparticular amount of time, then a reset unit 20 contained in the controlunit 26 resets the control unit to its starting position and thepreviously selected speed is cancelled so that the hand power drill canbe operated at a maximal possible speed. The period of downtime afterwhich the reset unit 20 resets the control unit 26 can be adjusted bymeans of an adjusting wheel 40 to a period from two to twenty minutes.

[0028] Instead of an adjusting wheel, it is also conceivable to providea different adjusting element deemed appropriate by one skilled in theart for adjusting the speed limitation, such as a switch rocker, one ormore actuating knobs, etc.

[0029] Reference Numeral List

[0030]10 housing

[0031]12 drive motor

[0032]14 adjusting device

[0033]16 adjusting device

[0034]18 reset unit

[0035]20 reset unit

[0036]22 spring element

[0037]24 adjusting element

[0038]26 electronic unit

[0039]28 switch

[0040]30 adjusting wheel

[0041]32 axle

[0042]34 housing part

[0043]36 gear

[0044]38 flange

[0045]40 adjusting wheel

[0046]42 leg

[0047]44 pin

[0048]46 pin

[0049]48 leg

[0050]50 pin

[0051]52 pin

[0052]54 ram

[0053]56 adjusting wheel

[0054]58 pulse generator

[0055]60 speed governor

[0056]62 power supply

[0057]64 line

[0058]66 display

1. A power tool, in particular a hand power tool, with a drive motor(12) disposed in a housing (10) and at least one adjusting device (14,16), which can be used to durably set at least one parameter of thedrive motor (12) and/or of a transmission during an operating phase,characterized in that the adjusting device (14, 16) has a reset unit(18, 20), which resets the adjusting device (14, 16) to a startingposition depending on at least one operating parameter.
 2. The powertool according to claim 1, characterized in that the adjusting device(14, 16) can set a maximal and/or minimal speed as a parameter.
 3. Thepower tool according to claim 1 or 2, characterized in that theadjusting device can set a maximal and/or minimal transmitted torque asa parameter.
 4. The power tool according to one of the preceding claims,characterized in that the reset unit (20) resets the adjusting device(16) depending on a period of downtime.
 5. The power tool according toclaim 4, characterized in that the reset unit (20) can adjust the periodof downtime after which the reset unit (20) resets the adjusting device(16).
 6. The power tool according to claim 4 or 5, characterized in thatthe period of downtime is between one minute and twenty minutes.
 7. Thepower tool according to one of the preceding claims, characterized inthat the reset unit (18, 20) resets the adjusting device (14, 16) when apower supply is interrupted.
 8. The power tool according to one of thepreceding claims, characterized in that the reset unit resets theadjusting device depending on a detected temperature value.
 9. The powertool according to one of the preceding claims, characterized in that thereset unit (18) has a mechanical reset mechanism.
 10. The power toolaccording to claim 9, characterized in that the reset mechanism resetsthe adjusting device (14) by means of a prestressed spring element (22).11. The power tool according to one of the preceding claims,characterized in that the restoring unit (18) has an electromagneticadjusting element (24).
 12. The power tool according to one of claims 1to 8, characterized in that the adjusting device (16) has at least oneelectronic unit (26), which is for adjusting the parameter and can bereset by means of the reset unit (20).